Yes. Bones are just Transforms, in Unity, so you can alter their rotations (although I think positions would be what you need for a sine wave, unless I'm misunderstanding the effect) as you like. Transform.Find will probably help you most, in acheiveing this, because unless you create the mesh procedurally in Unity, you won't know what is what, in the SkinnedMeshRenderer.bones array.

when trying to assign the Transform.Find to a variable, like the example in the link, I get an error "ArgumentException: You are not allowed to call get_transform when declaring a variable. Move it to the line after without a variable declaration."